The field of the invention relates to methods of improving performance of anaerobic digester systems, otherwise referred to as “bioaugmentation.” In particular, the field of the invention relates to bioaugmentation of anaerobic digester systems in order to improve performance parameters related to production of methane, reduction in effluent chemical oxygen demand (COD) or recovery from organic overload.
Methane is a commercially valuable fuel, as well as synthetic precursor, and can be obtained via microbial fermentation processes. In addition, proper methane production is required for stabilization of municipal, industrial and agricultural wastes via anaerobic digestion. Many euryarchaeotal microorganisms can use hydrogen and carbon dioxide to produce methane.
Anaerobic digester systems are used to treat wastes and produce renewable energy. In the process, select microorganisms are contacted with the waste and convert it to biogas that contains methane. The methane can be used as a renewable fuel.
Anaerobic digestion is a multistep process with different microbial communities working in syntrophy. If the syntrophy is disrupted by organic overload or other changes, then the entire process may slow or stop, causing costly delays at agricultural, industrial, and municipal treatment plants. Most notably, efficient metabolism of hydrogen (H2) and propionic acid is required. Propionate and H2 accumulation have been seen as an indicator of process imbalance (McCarty and Smith, 1986).
Propionate accumulation is an indicator of process imbalance in organically overloaded anaerobic digesters. Following the overload, methane production can take months to recover. Upset of anaerobic digesters due to an organic overloading is a common problem in the field, and practical methods to reduce recovery time would be beneficial and of commercial value.
Practical methods to reduce recovery time of upset digesters would be beneficial and commercially valuable. One potential method is “bioaugmentation,” the addition of specific, active microbes to enhance performance. Regarding anaerobic digestion, no published reports of full-scale applications were found; however, reports of laboratory studies describe bioaugmentation to improve degradation of specific chemicals, digester startup, recovery of stressed digesters, and odor reduction (e.g., Saravanane et al., 2001).
Oxygen (O2) toxicity tolerance of anaerobic cultures used for bioaugmentation is of particular importance. Methanogenic cultures that are resistant to O2 toxicity may be better choices as bioaugmentation cultures since they may contain unique, beneficial microbial communities or be more easily freeze-dried, stored and transported in an air atmosphere.
Currently, very little attention is paid to the exact microorganisms used during anaerobic (or aerobic) digestion. Likewise, little attention is paid to the digester microbial community structure, and the relationship between community structure and digester performance. When a digester is started, it is common practice to obtain starter culture from the most near-by operating digester system and the exact microbes present are not determined. Regarding performance, some digester systems may not produce as much biogas as possible, and other digesters may loose biogas production due to changes in feed waste composition, temperature, or other factors. As such, methods for enhancing performance of anaerobic digester systems are desirable including methods of bioaugmentation.